Method of and apparatus for manufacturing integral finned tubing

ABSTRACT

A method of forming integral helically finned tubing utilizes forming rolls each of which has a plurality of annular projections of graduatedly increasing radius. Each roll is mounted on and drivable by a shaft which is inclined to the work axis at an angle corresponding to the intended helix angle of the fins. The shaft is spaced from the work by a fixed radial distance which corresponds to that for full working engagement between the rolls and the work. The rolls are fed longitudinally of the axis of the shaft from a position clear of the work into engagement with the work to progressively engage the projections of increasing radius with the work as the work feeds in the direction toward the larger projections.

ilite States Patent 1 Novak [451 Dec. 24, 1974 METHOD OF AND APPARATUS FOR MANUFACTURING INTEGRAL FINNED TUBING [76] Inventor: Arthur H. Novak, 29900 Woodland Dr., Southfield, Mich. 48075 [22] Filed: Jan. 21, 1974 [21] Appl. No.: 434,955

Primary Examiner-Lowell A. Larson Attorney, Agent, or FirmHarness, Dickey & Pierce 5 7 ABSTRACT A method of forming integral helically finned tubing utilizes forming rolls each of which has a plurality of annular projections of graduatedly increasing radius. Each roll is mounted on and drivable by a shaft which is inclined to the work axis at an angle corresponding to the intended helix angle of the fins. The shaft is spaced from the work by a fixed radial distance which corresponds to that for full working engagement between the rolls and the work. The rolls are fed longitudinally of the axis of the shaft from a position clear of the work into engagement with the work to progressively engage the projections of increasing radius with the work as the work feeds in the direction toward the larger projections.

3 Claims, 4 Drawing Figures METHOD OF AND APPARATUS FOR MANUFACTURING INTEGRAL FINNED TUBING BACKGROUND OF THE INVENTION Tubing having integral fins has been produced heretofore by subjecting a length of tubular stock to the action of a set of forming rolls. Typically, three rolls equally spaced around a straight length of tube to be finned are employed, each roll being mounted on a head for movement substantially radially into and out of engagement with the stock. Each forming roll has a plurality of axially spaced annular work-forming projections of graduated diameter. The axes of the arbors are inclined with respect to the axis of the stock at an angle corresponding to the desired helix angle of the fin to be formed. The rolls are rotated around their individual axes to cause the work to rotate and to feed in a direction toward the larger work-forming projections.

With such prior apparatus, when the rolls are moved radially inwardly into engagement with the stock, the larger projections engagethe work before the smaller projections. During the interval required to move the rolls into full engagement, partial fins of increasing depth are formed. This tapered area of incomplete finning is of a length which depends largely upon the speed of rotation and feed of the work. When finning at high rotational speeds with multiple fin starts (multiple helices), such tapered sections have been longer than is desirable. The heat transfer capacity of such tapered sections is of course lower than optimum.

In addition, due to the fact that the larger projections engage the work first, there is a tendency with such prior apparatus to work the stock more severly with the leading large projections. In effect, the first-engaging projections are required to work harder than normal during feed-in of the rolls, causing excessive work hardening and tending to trap metal behind them. Such metal is deformed in a localized area to form an initial hump-like fin section of greater than normal height, while in addition the excessive work hardeningof the metal of the stock increases the load upon the following projections of lesser height.

The overall object of the present invention can be summarized as to overcome the aforementioned shortcomings of existing methods and to provide an improved method and apparatus for forming at high rotational speeds on thin walled tubing closely spaced fins having a multiplicity of leads while still obtaining short transition tapers from plain sections of the tubing to full fin depth.

Another object is to provide such an improved method and apparatus which eliminates the aforementioned oversize fin diameter or hump" characteristic of finned tube transition portions when manufactured with such prior known apparatus.

A further object is to provide an improved method of the character indicated which is adapted to be performed by simplified machinery.

Other objects will become apparent upon consideration of the present disclosure in its entirety.

BRIEF DESCRIPTION OF THE FIGURES OF DRAWING FIG. I is a plan view of apparatus used in connection with the present invention, showing a portion of a tube to be finned and a forming roll in the start position;

FIG. 2 is an elevational view of the same in the start position;

FIG. 3 is a plan view of the roll and tube in the rolling position; and

FIG. 4 is an elevational view of the roll and tube in the rolling position.

DETAILED DESCRIPTION OF THE PREFERRED FORM OF THE INVENTION Reference character 10 designates generally a forming roll, comprised, in the instance depicted, of a plurality of discs of graduatedly increasing diameter and the peripheral work-engaging portions of which are contoured in a known manner to progressively deform the tube Wto be worked on so as to extrude fins outwardly from the material of the tube. Five discs, 1 1, 12, 13, 14 and 15 are shown, although a greater number are normally used. The details as to number and form of the discs do not form a part of the present invention, and in fact the annular work-forming projections which constitute the peripheral portions of the discs could be formed as integral contourings of a solid roll.

As indicated previously, the finning operating is performed by a plurality of such rolls, typically three in number, arranged around the work. When engaged with the work, the inclination of the forming discs to the axis, and the spacing between the work-forming projections of the discs, are such that each disc subsequent to the leading disc 1 1 engages and performs additional deforming work upon an area worked upon by the preceding disc of the set. As is also well knwon in the art, the discs and the inclination to the axis may be so arranged that they form either a single helical fin or multiple sets of helices (Multiple start" finning). The multiple start method is preferred, since it permits a more rapid operation.

The work tube W may be supported on and backed by a suitable internal mandrel 16 in accordance with known practice. I

All of the rolls of the set are arranged for simultaneous operation. Only a single' roll and spindle are shown, since all are alike, but each roll, as shown in the drawing, is fast on a spindle or arbor S. The spindles are simultaneously synchronously rotatable in the same angular direction, and cause the work to rotate and to advance due to the frictional engagement between the rolls and the work. Each of the spindles is supported upon a fixed axis, but the spindles, and the rolls carried thereby, are movable in a straight path, longitudinally of the spindle axes, to move the rolls between a retracted or start position, shown in FIGS. 1 and 2, in which they are clear of the work, and the working position shown in FIGS. 3 and 4, in which they are in a fully engaged and effectively meshed work-forming relation with the work.

The work travels from right to left, as viewed in the drawing, while the work rolls are fed into the work from left to right. By reason of the fact that the smaller projections engage the work first, there is no entrapment of metal such as causes the hump previously referred to, and the transition between the smooth tube area 20 (which may, for example, be for connection purposes) shown at the left in FIG. 4 and the subsequent threaded area 22, is abrupt. In addition, there is no initial excessive work hardening such as occurs where the rolls are moved into the work radially.

Upon completion of the desired length of finning, the rolls are moved back from the work in the opposite direction as the feed-in (denoted by the arrow F in FIG. 1) until the rolls are entirely clear of the work, which is then removed from the mandrel, whereafter the rolls are back in the starting position corresponding to that shown in FIG. 1, ready for the next workpiece. Although the rolls could be withdrawn from the work radially, rather than by moving them backward along the same path as the in-feed, that is, along the same line substantially perpendicular to the helix angle, it will be recognized that radial withdrawal would leave a tapered effect comprised of some incomplete fins at the trailing end of the tube.

With the prior known feed arrangement in which the rolls are fed into and retracted from the work substantially radially, the elongation effect on the work is variable and much mismatching of grooves takes place until the rollers reach their full working depth. With my improved method, the feed of the rolls into the work can be so timed that when the largest disc reaches full depth, the first area contacted by the smallest disc 11 reaches the largest disc. Thus, uniform, full-height fins can be formed commencing practically at the point of initial contact. Also, the work hardening is gradually and progressively increased, from zero at the initial point of contact toward the full unavoidable amount of work hardening caused by the subsequent rolls. Excessive work hardening by the initial contacting disc, and entrapment of metal, are thus effectively eliminated.

It should be understood that although the invention has been described as having driving means for the rolls, and the work tube described as driven by the rolls, this driving arrangement might be reversed; that is, the tube might be rotated to turn the rolls. The principle of operation remains the same in such case, but machine design is less convenient since the tube (or rolls) must also be free to move axially of the tube.

This Detailed Description of the Preferred Form of the Invention, and the accompanying drawings, have been furnished in compliance with the statutory requirement to set forth the best mode contemplated by the inventor of carrying out the invention. The prior portions consisting of the Abstract of the Disclosure" and the Background of the Invention" are furnished without prejudice to comply with administrative requirements of the Patent Office.

I claim:

1. The method of making finned tubing which comprises providing a tube to be finned and which is rotatable about a fixed axis, providing a forming roll having a series of annular forming projections thereon of sequentially increasing diameter, the tube also being movable longitudinally of its axis relatively to the roll, driving the roll rotatably about an axis which is inclined with relation to the axis of the tube and which is spaced from the tube at a fixed distance such that when the roll is at the closest crossing point of such axes the projections are in full working engagement with the tube, characterized by moving the roll longitudinally of its axis of rotation from a start-position in which the roll is disengaged from the tube to said position of full engagement and maintaining such full engagement while driving the roll and tube in synchronous meshed engagement about their respective axes and permitting the tube to move longitudinally of its axis relatively to the rolls, whereby the projections deform a helical section of the tube, the path of longitudinal movement of the points of engagement of the projections with the tube, during feeding of the roll into such full engagement, being substantially perpendicular to the helix angle.

2. A method as defined in claim 1 in which the projections are of increasing diameter along the axis of rotation of the roll in a direction away from the tube when the roll is in the start position, whereby a projection of smallest diameter engages the tube first, followed by projections of successively increasing diameter.

3. A method as defined in claim 2 wherein the roll is disengaged from the work by moving it back along the axis of rotation of the roll in a direction toward the start position. 

1. The method of making finned tubing which comprises providing a tube to be finned and which is rotatable about a fixed axis, providing a forming roll having a series of annular forming projections thereon of sequentially increasing diameter, the tube also being movable longitudinally of its axis relatively to the roll, driving the roll rotatably about an axis which is inclined with relation to the axis of the tube and which is spaced from the tube at a fixed distance such that when the roll is at the closest crossing point of such axes the projections are in full working engagement with the tube, characterized by moving the roll longitudinally of its axis of rotation from a start-position in which the roll is disengaged from the tube to said position of full engagement and maintaining such full engagement while driving the roll and tube in synchronous meshed engagement about their respective axes and permitting the tube to move longitudinally of its axis relatively to the rolls, whereby the projections deform a helical section of the tube, the path of longitudinal movement of the points of engagement of the projections with the tube, during feeding of the roll into such full engagement, being substantially perpendicular to the helix angle.
 2. A method as defined in claim 1 in which the projections are of increasing diameter along the axis of rotation of the roll in a direction away from the tube when the roll is in the start position, whereby a projection of smallest diameter engages the tube first, followed by projections of successively increasing diameter.
 3. A method as defined in claim 2 wherein the roll is disengaged from the work by moving it back along the axis of rotation of the roll in a direction toward the start position. 